FIGS. 1A to 1D are diagrams illustrating a method of fabricating a field effect high frequency semiconductor device, such as a high electron mobility transistor (HEMT) or a metal-semiconductor field effect transistor (MESFET), in the related art.
First, as illustrated in FIG. 1A, an active region is defined by dry etching a semiconductor substrate having a structure in which an SiC substrate 101, an AlN buffer layer 103, a non-doped GaN channel layer 105, a non-doped AlGaN spacer layer 107 and a non-doped AlGaN Schottky layer 109 are stacked.
Subsequently, as illustrated in FIG. 1B, an ohmic metal electrode 111 is formed, PMMA and co-polymer resist are applied, and then an exposure is performed through an electron beam lithography method, to form a T-shaped resist pattern 113.
Next, as illustrated in FIG. 1C, a gate metal 115 formed of Ni/Au is deposited using vacuum deposition equipment, and when the resist pattern 113 is removed through a lift-off process, a T-shaped gate electrode 117 illustrated in FIG. 1D is completed.
However, in the semiconductor device fabricated through the aforementioned method in the related art, the T-shaped resist pattern is formed using the PMMA and the co-polymer. Accordingly, when a T-shaped gate electrode having a fine gate length is formed, there is a problem in that gate metal is not uniformly deposited in a vicinity of a narrow opening of the gate pattern. When the gate metal is thickly deposited in order to reduce resistance of the gate electrode, a temperature of the vacuum deposition equipment rises such that the resist pattern becomes deformed, thereby failing to stably form the T-shaped gate electrode.
When a high-frequency semiconductor device is fabricated using the existing T-shaped gate electrode, a high electric field is generated between the gate electrode and the drain electrode, so that breakdown voltage of the semiconductor device is decreased and the reliability of the device is deteriorated.